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Biomedical subjects

A Santini

Publications and source records attributed to A Santini.

At least 73 records · Page 4Linked to original sources
PubMed1990

Critical main-chain length for conformational conversion from 3(10)-helix to alpha-helix in polypeptides.

To assess the minimal peptide length required for the stabilization of the alpha-helix relative to the 3(10)-helix in Aib-rich peptides, we have solved the X-ray diffraction structures of the terminally blocked sequential hexa- and octapeptides with the general formula-(Aib-L-Ala)n-(n = 3 and 4, respectively). The hexapeptide molecules are completely 3(10)-helical with four 1----4 intramolecular N-H . . . O = C H-bonds. On the other hand, the octapeptide molecules are essentially alpha-helical with four 1----5 H-bonds; however, the helix is elongated at the N-terminus, with two 1----4 H-bonds, giving these molecules a mixed alpha/3(10)-helical character. In both compounds the right-handed screw sense of the helix is dictated by the presence of the Ala residues of L-configuration. This study represents the first experimental proof for a 3(10)----alpha-helix conversion in the crystal state induced by peptide backbone lengthening only.

Chemical Phenomena↗
PubMed1989

Rate of formation of tertiary dentin in dogs' teeth in response to lining materials.

The rate of tertiary dentin produced in response to four lining materials placed in standardized cavities in dogs' teeth was measured over a period of 119 days. Sterile denatured dentin ash was used as a control material in an attempt to quantify tertiary dentin formation in response to cavity preparation. In all periods the amounts of tertiary dentin formed beneath the control material were significantly smaller than those formed beneath any of the four lining materials. In the first 98 days the rate of formation of tertiary dentin beneath calcium hydroxide (Calxyl) was significantly greater than that beneath the material containing corticosteroid (Ledermix cement). In the last 21 days there was no difference in daily rates of tertiary dentin production beneath all of the lining materials. With all the lining materials there was a highly significant difference between the daily amounts of tertiary dentin formed in the first 6 weeks and those in the last 11 weeks.

Animals↗
PubMed1989

Structural versatility of peptides containing C alpha, alpha-dialkylated glycines: conformational energy computations, i.r. absorption and 1H n.m.r. analysis of 1-aminocyclopropane-1-carboxylic acid homopeptides.

Conformational energy computations on the 1-aminocyclopropane-1-carboxylic acid mono-, di-, and tripeptide amides, Ac-(Ac3c)n-NHMe (n = 1-3), indicate that this C alpha, alpha-dialkylated, cyclic alpha-amino acid residue is conformally restricted and that type-I(I') beta-bends and distorted 3(10)-helices are particularly stable conformations for the di- and tripeptide amides, respectively. The results of the theoretical analysis are in agreement with those obtained in an i.r. absorption and 1H n.m.r. investigation in chloroform solution of Ac3c-rich tri- and tetrapeptide esters. A comparison is also made with the conclusions extracted from our previous work on peptides rich in Aib (alpha-aminoisobutyric acid), Ac5c (1-aminocyclopentane-1-carboxylic acid), and Ac6c (1-aminocyclohexane-1-carboxylic acid).

Alkylation↗
PubMed1989

Structural versatility of peptides containing C alpha, alpha-dialkylated glycines. An X-ray diffraction study of six 1-aminocyclopropane-1-carboxylic acid rich peptides.

The molecular and crystal structures of six fully blocked, Ac3c-rich peptides to the tetramer level were determined by X-ray diffraction. The peptides are Fmoc-(Ac3c)2-OMe-CH3OH, Ac-(Ac3c)2-OMe, t-Boc-Ac3c-L-Phe-OMe, pBrBz-(Ac3c)3-OMe.H2O, Z-Gly-Ac3c-Gly-OTmb.(CH3)2CO, and t-Boc-(Ac3c)4-OMe.2H2O. Type-I (I') beta-bends and distorted 3(10)-helices were found to be typical of the tri- and tetrapeptides, respectively. In the dipeptides, too short to form beta-bend conformations, other less common structural features may be observed. The average geometry of the cyclopropyl moiety of the Ac3c residue is asymmetric and the N-C alpha-C' bond angle is significantly expanded from the regular tetrahedral value. A comparison with the structural preferences of other extensively investigated C alpha, alpha-dialylated alpha-amino acids is made and the implications for the use of the Ac3c residue in conformational design are examined.

Alkylation↗
PubMed1989

Effects of two different hydrocortisone doses on human peripheral blood lymphocyte nucleologram.

The effect of 200 and 500 mg of hydrocortisone hemisuccinate given i.v. on the circulating lymphocyte nucleologram was studied in 12 healthy volunteers. Transient lymphopenia was observed in all treated subjects, with the nadir at 3 to 9 h after drug administration. An evaluation of the lymphocyte nucleologram, at this time, showed a statistically significant decrease in mono- and binucleolated lymphocytes. By 24-36 h, the number of total lymphocytes and the nucleologram had returned to baseline values. No differences were revealed among the two groups of subjects. The role of lymphocyte redistribution and of lymphocytolysis to explain the lymphocytopenia and the behaviour of lymphocyte nucleologram is discussed.

Adult↗
PubMed1987

Tissue response to retrograde root fillings in the ferret canine: a comparison of a glass ionomer cement and gutta-percha with sealer.

Tissue healing was compared after apicectomy and filling of ferret lower canines with glass ionomer (Ketacfil) or gutta-percha/sealer (Tubliseal). Both materials provoked an inflammatory response after 7 days, but the response to glass ionomer was less severe. The response after 28 days was different. Mild inflammation related to the gutta-percha was still present, but no inflammation was found in relation to the glass ionomer. Bone infill was quite advanced in all specimens at 28 days but was more complete in the glass ionomer specimens, with intimate contact between the bone and cement.

Animals↗
PubMed1986

Nucleologram variations in circulating lymphocytes after chemotherapy.

The lymphocyte nucleologram of cancer patients was studied before and after chemotherapy. Drug treatment was constantly followed by morphological and numerical changes in lymphocyte nucleolar pattern, characterized by an increase in micropolynucleolated forms. This variation is a non-specific marker of drug cytotoxicity.

Aged↗